ABSTRACT
In interventional medical procedures,
other than the highly important issue of optimizing image quality and patient
exposure using the primary beam, there remains a continuing need for the study
of staff exposure from the scattered radiation. Herein, investigation is made
of the 3D stray-radiation distribution, the simulation being made of a
realistic interventional scenario through use of the Monte Carlo code Geant4
(version 10.3). The simulation is conducted based on the high definition
reference Korean-man (HDRK-man) computational phantom and a GE Infinia 3/8” C-arm machine, focusing on the effect of variation
of kVp and field of view (FoV) on the scattered particles’ spatial
distribution. With direct measurement of the absorbed dose remaining
challenging, not least in respect of the organs at risk, we computed the
scatter fractions,
defined as the ratio of the air kerma free-in-air to the entrance surface air
kerma (ESAK), which are both easily quantifiable. Scatter fraction
distributions were simulated for X-ray tube outputs (and half-value layers,
HVL) of 60 kVp (2.3 mm Al),
80 kVp
(3.2 mm Al)
and 120 kVp (4.3 mm Al)
and FoV of 15, 20, 25 and 30 cm. The
distributions are obtained for different height levels, corresponding to the
lens of the eye, and the lung and prostate, all radiosensitive organs.
Investigations are made for eight likely locations around the patient. At fixed
FoV results reveal an inverse relationship between ESAK and kVp, also that
change in kVp from 60 to 80 has a greater effect than from 80 to 120. For
change in FoV at fixed kVp, the scatter fraction remains constant. The
particular staff locations are found to be optimal in seeking mitigation of
dose. Moreover, the combined usage of numerical human model and Monte Carlo
simulation can be considered as an added value to the radiation safety research
field, especially to the interventional radiology staff and to the patient.